For example, when controlling the flow rate of aeration air supplied to an aeration tank to promote biological reaction in a sewage treatment plant provided with a biological reaction tank, a flow rate control method controls the flow rate of aeration air in proportion to the inflow of sewage. However, reaction rate is dependent on the quality of water and hence the feed forward flow rate control method is unable to control the flow rate properly and to reduce the cost.
In another treatment process, such as a returned sludge quantity control, processes are controlled individually. However, the control of the general operation of the sewage treatment plant for the stabilization of water quality and the reduction of processing costs has not been conducted.
The improvement of the quality of treated water (observation of standards) is desired for the maintenance of environmental water condition. However, the currently used control method requires much water disposal costs and it has been desired to control water quality capable of reducing treatment costs, maintaining satisfactory water quality. The general operation and control of a water sewage treatment plant have been desired.
However, as mentioned previously, any control for stabilizing water quality and reducing treatment costs has not been achieved.